1. Field of the Invention
This invention relates to a process for the production of new, unsaturated urethanized polyester resins, to the polyester resins obtained by this process and to coatings prepared from coating compositions based on these polyester resins and cured by free radical polymerization, especially coatings for wood or wood-like materials.
2. Description of the Prior Art
Unsaturated polyester resins are known as binders for coating compositions. They are cured by free radical polymerization. The polymerization is initiated either by redox systems, such as metal salts or hydroperoxides, or by UV irradiation in the presence of a photoinitiator. Since the coating compositions are mainly intended for wood and wood-like materials, they can only be cured at temperatures from room temperature to at most 80.degree. C. At these temperatures, the curing times are longer than those of other paint film binders. For example, coatings which dry purely physically (by evaporation of the solvent) cure much more quickly than coatings based on unsaturated polyester resins.
However, these faster drying coatings do not achieve the property level of coatings produced from unsaturated polyester resins as binders.
Numerous attempts have already been made to modify the unsaturated polyester resins in such a way that faster curing rates are obtained. Thus, as described for example in DE-OS 2 360 366 or DE OS 1 520 695, unsaturated polyester resins are reacted with isocyanates. This reaction provides products of relatively high viscosity with improved, but still inadequate curing times.
Special polycyclic alcohols are capable, when used as an esterification component in unsaturated polyester resins, of imparting a tack-free paint film surface to the unsaturated polyester resins after curing despite the presence of atmospheric oxygen (see Wagner-Sarx: "Lackkunstharze", Carl Hanser Verlag, Munchen, 1971, page 138). However, the coatings generally show inadequate hardness and, in addition, are not resistant to solvents.
Accordingly, an object of the present invention is to provide new polyester resins which are not attended by the disadvantages mentioned above, i.e., are suitable for the production of free radical-curing coating compositions, which cure quickly both under UV irradiation and with the aid of peroxides and provide coatings having hard surfaces which are resistant to water and chemicals.
Surprisingly, this object may be achieved by the process according to the invention which is described in more detail hereinafter. In this process certain olefinically unsaturated polyester resins A) are reacted with certain polyisocyanates B) in specific quantitative ratios.